1. Field of the Invention
The invention relates to a cell for testing geomaterials on cylindrical specimens, in particular rock, ground, or materials manufactured on sampling sites. In particular, the cell will enable to subject the specimen at least to a simple compression or still to subject the specimen to a triaxial test.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
In the field of the geomaterials, triaxial cells, such as for example those disclosed in document FR-2.663.121 are known, which enable to subject a cylindrical specimen to different pressure, loading, temperature and draining conditions. The cell and the specimen are to that end fitted with different sensors, such as for example pressure, temperature, displacement sensors.
The triaxial cell generally comprises a cell body with an internal cavity forming a sealed chamber inside which the cylindrical specimen is placed vertically. A controlled pressurising or draining hydraulic circuit is connected to the sealed chamber for subjecting the lateral wall of the specimen to a radial stress to the pressure of a fluid. Quite often, this constraint is applied through an elastic envelope hugging and protecting the lateral wall of the specimen.
In the sealed chamber, a lower plate and an upper plate may be brought closer to and apart from one another for constraining the specimen along its longitudinal axis or conversely for unloading it.
The lower plate may be fixed relative to the stand formed of a lower mount of the cell body, wherein the upper plate is compelled to move under the action of a piston capable of sliding through the upper wall of the body.
During the tests, it is thus possible to subject the specimen to a simple compression or still to a triaxial test, wherein the specimen is compressed along its longitudinal axis and a radial stress is exerted simultaneously on the lateral wall of the specimen, under the action of a fluid. In the case of a triaxial test notably, it is also possible to subject the specimen to draining conditions so as to study its permeability.
For the loading/compression, possibly permeability tests, it may prove interesting to study a cracked specimen.
Today, so as to obtain the cracked specimen, the specimen is broken previously to the testing phase, thereby creating the crack artificially. In practice, the specimen is broken in two and reconstructed in the test cell. It should be noted that the onset of the crack on the specimen is controlled rather poorly.
U.S. Pat. No. 3,406,567 discloses a portable testing device for measuring the shearing load of a cylindrical specimen, snow or ground.
This device comprises a hollow, rigid cylinder for receiving the specimen, as well as a pair of matrices, respectively sliding at the level of the ends of said hollow cylinder. To that end, each matrix, whose section is adjusted to the inside diameter of the hollow cylinder, exhibits a nipple for engaging into a guiding slot of said hollow cylinder.
The contact surface of the matrix with the specimen, semi-circular in section, only extends over half the matrix, wherein the other half has a cavity so as not to touch the specimen on this area. Both matrices are arranged, relative to each other in an offset manner.
One of the lower matrices rests on the stand of the device, wherein the other matrix is mobile relative to this mount by means of a jack for constraining the specimen.
During testing, it is then possible to constrain the specimen until said specimen cracks. the shearing load can be measured especially by analysing the load-time curve.
However, once the specimen has been cracked in two parts, such a device hardly enables control of the relative displacement between both parts.
The aim of the present invention is to remedy the drawbacks aforementioned while offering a test cell enabling to crack the specimen in situ, while restricting the relative displacement of the cracked parts.
Another aim of the present invention is to be able to control the positions of the crack at least at the ends of the specimen.
Another aim of the present invention is to offer a cell at least enabling to subject the specimen to a simple compression test.
Another aim of the present invention is to offer a cell enabling to subject the specimen to a triaxial test.
Another aim of the present invention is to offer a cell for conducting permeability tests on the cracked specimen.
Other aims and advantages of the present invention will appear in the following description which is given only by way of example and without being limited thereto.